Old TORO

Since 2006, the year in which TORO objectives were modified, the TORO OS project corresponding to the version 1.xx was discontinued. These versions achieved a great success in terms of functionality. The most stable version was 1.1.3, sometimes I see the source of those versions and I feel very sorry of have abandoned it, however it was impossible to me to continue with both projects simultaneously. So I decided to make a small tribute to those versions. For that i will show next how to test TORO 1.1.3 through BOCHS. I've put some screenshots for you to observe the beauty of a shell in PASCAL. Enjoy it!

For these simulations is necessary x86 Bochs, remember that the 1.1.3 version is only for 32 bits. Here I include the torobch.bxrc file contents.

megs: 256

romimage: file=BIOS-bochs-latest, address=0xf0000

floppya: 1_44=toro-1.1.3.img, status=inserted

boot: floppy

It is necessary to download the toro-1.1.3 image from the link:

http://sourceforge.net/projects/toro/files/images/toro-1.1.3/toro-1.1.3.img/download

If everything is allright, the first window you will see when execute BOCHS will be:

Corresponds the GRUB bootloader, there you select TORO-1.1.3 and press enter.

It will start to load the OS and then the Shell:

We are ready to enter commands on TORO. The first command we will see is the ls that, as you already know, lists the actual directory.

Now we go to the directory where finds TORO's source using cd.

And we are going to run echo printk.pas, this will display the file content on screen.

You can see all Shell commands at /BIN directory, these are:

Running reboot the system is closed and we can turn off the virtual machine.

I hope you enjoyed it, make your own experiences running commands. You can also burn the image in a 3 ½ floppy and try it in a real machine.

Attention: Versions 1.x.x have no relation with version 0.xx, they are different things.

Matias E. Vara

www.torokernel.org

Toro Builder uploaded!

I uploaded the new interface for Toro developing. You can compile and debug the kernel easy using ECLIPSE and QEMU, for download go here but first read the new WIKI for more information. I am working hardly for write usefull information.
If someone wants to be an EDITOR of WIKI contact me to torokernel@gmail.com, saludos.

Matias E. Vara
www.torokernel.org

Context Switching

In this article I will try to make a brief description about “Context Switching” and specially how TORO implements it since version 0.01. I won’t talk about how TORO OS implements it in versions 1.xx, I’ll just say that it uses “Context Switching” by hardware. In future articles I will show the implementation of these ideas on pascal. If you have doubts, see the references! Enjoy it!

As we know, in kernel, the scheduler is in charge of thread distributions. A part of implementing the scheduling algorithm it performs the "Context Switching" procedure. When selects a new thread, the scheduler fills the processor registers with the values that they had just before the thread invokes the kernel (NOTE this comment is related with TORO’S scheduling algorithm, which is the cooperative thread).

Figure 1. Procedure for loading a new process.

In the x86-64 architecture some of the general use registers are RAX, RBX, RCX, etc. In addition to these registers, some system registers must be also updated, like CR3. These ones store information about the thread page directory that will be loaded. The procedure is named "Context Switching " and is a critical operation because it runs continuously so it must be very fast.

The “Context Switching” procedure can be implemented by software and by hardware.

When it’s implemented by hardware, it uses the mechanisms that provide a particular architecture for make the “Context Switching “. For example, for the x86 architecture, are used the structures named “tasks descriptors”, these ones are in the GDT (Global Descriptor Table) and when a new task must be loaded is simply used the instruction "call" to the task descriptor (called in the literature as TSS) [1].

On the other hand, in the implementation by software the “Context Switching” is done "by hand" and is a routine written by the programmer the one in charge of saving the value of the registers.

At first glance the “Context Switching” by hardware seems to be the best option because the programmer isn’t involved and is done "automatically". Often, in the “Context Switching” by hardware, registry values are all saved, but sometimes are not being used all records. That’s why the implementation by hardware may not be the best option.

For this reason the “Context Switching” in TORO is implemented by software, programming techniques are used for not using the “Context Switching” mechanism that offers a particular hardware. When the scheduler selects a new thread, it loads in the processor's registers the values corresponding to the new thread, and then starts run. The thread begins its execution after the moment when the SysThreadSwitch procedure was called.

As the “Context Switching” is always done after invoke the SysThreadSwitch function, the planner supposes that at that moment the processor's registers are not being used by the user application. In this way it's limited only to save the state of the stack's thread that has to be removed. For the implementation on x86-64 architecture, this is achieved by saving on the TThread structure the RSP registry value, wich keeps its position inside the stack.

The “Context Switching” implemented in TORO is faster than the one by hardware and the one implemented on an OS for general purposes. The selection of the “Context Switching” method is directly related to the cooperative thread model.

Therefore the utilization of “Context Switching” by software adds portability and speed [2].

[1]. Intel. IA-32 Intel® Architecture Software Developer’s Manual. Vol3. 2004.

[2]. Osdev Wiki, Context Switching, http://wiki.osdev.org/Context_Switching.

Matias E. Vara

www.torokernel.org

Changes on SVN

I ´ll work on SVN directories so maybe it ´ll be off-line a few hours. You should make an update on SVN.

Saludos
Matias E. Vara
www.torokernel.org